CVE-2023-39363: Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine (EVM). In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are ...

Description

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine (EVM). In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are allocated incorrectly. Each function using a named re-entrancy lock gets a unique lock regardless of the key, allowing cross-function re-entrancy in contracts compiled with the susceptible versions. A specific set of conditions is required to result in misbehavior of affected contracts, specifically: a `.vy` contract compiled with `vyper` versions `0.2.15`, `0.2.16`, or `0.3.0`; a primary function that utilizes the `@nonreentrant` decorator with a specific `key` and does not strictly follow the check-effects-interaction pattern (i.e. contains an external call to an untrusted party before storage updates); and a secondary function that utilizes the same `key` and would be affected by the improper state caused by the primary function. Version 0.3.1 contains a fix for this issue.

Metrics

CVSS 3.1

5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS 4.0

9.1/10

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H/E:A/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.71%

48.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-863

Affected Software

Vendor	Product	Versions
Vyperlang	Vyper	0.2.15
Vyperlang	Vyper	0.2.16
Vyperlang	Vyper	0.3.0

References

https://github.com/vyperlang/vyper/pull/2439Patch
https://github.com/vyperlang/vyper/pull/2514Patch
https://github.com/vyperlang/vyper/security/advisories/GHSA-5824-cm3x-3c38Exploit, Patch, Third Party Advisory
https://hackmd.io/@LlamaRisk/BJzSKHNjnExploit, Third Party Advisory
https://hackmd.io/@vyperlang/HJUgNMhs2Exploit, Third Party Advisory
https://github.com/vyperlang/vyper/pull/2439Patch
https://github.com/vyperlang/vyper/pull/2514Patch
https://github.com/vyperlang/vyper/security/advisories/GHSA-5824-cm3x-3c38Exploit, Patch, Third Party Advisory
https://hackmd.io/@LlamaRisk/BJzSKHNjnExploit, Third Party Advisory
https://hackmd.io/@vyperlang/HJUgNMhs2Exploit, Third Party Advisory

Timeline

Published: Aug 7, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-39363?

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine (EVM). In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are allocated incorrectly. Each function using a named re-entrancy lock gets a unique lock regardless of the key, allowing cross-function re-entrancy in contracts compiled with the susceptible versions. A specific set of conditions is required to result in misbehavior of affected contracts, specifically: a `.vy` contract compiled with `vyper` versions `0.2.15`, `0.2.16`, or `0.3.0`; a primary function that utilizes the `@nonreentrant` decorator with a specific `key` and does not strictly follow the check-effects-interaction pattern (i.e. contains an external call to an untrusted party before storage updates); and a secondary function that utilizes the same `key` and would be affected by the improper state caused by the primary function. Version 0.3.1 contains a fix for this issue.

How severe is CVE-2023-39363?

CVE-2023-39363 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 0.71% probability of exploitation in the next 30 days.

How do I fix CVE-2023-39363?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.